1. Field of the Invention
This invention relates to electric motors, especially those for directly driving rotary loads requiring "clean room" conditions, such as do many information storage disks.
2. Description of the Related Art
In the market for information storage disks, there is a continuing demand for compactness. Earlier, this demand was satisfied by external rotor motors, which could be axially relatively short. Now that demand is also directed toward an ever-diminishing diameter of information storage disks and of the apparatuses which hold them. At the same time, the motor must still supply adequate torque, have a certain minimum angular momentum and smooth-running operation, and inhibit the passage of dirt particles from its bearings and torque-generating regions toward a "clean room" region, all without increasing its overall axial dimension.